React component not rendering after state change

Question

As the title says, when my state changes in my component, the sub components aren't rerendering.

  class App extends Component {
    constructor() {
      super()
      this.state = {
        url: ""
      }
      this.handleWorkerSelect = this.handleWorkerSelect.bind(this)
    }
    handleWorkerSelect(url) {
      this.setState({ url })
    }
    render() {
      return (
        <div className="App">
          <Workers className="workers" handleClick={this.handleWorkerSelect}/>
          <HermesWorker url={this.state.url}/>
        </div>
      )
    }
  }

  const Workers = (props) => {
    return (
      <div>
        <button onClick={() => props.handleClick("http://localhost:5000/api")}>Worker 1</button>
        <button onClick={() => props.handleClick("http://localhost:2000/api")}>Worker 2</button>
      </div>
    )
  }
  export default App

here is hermesworker.js

class HermesWorker extends Component {
    constructor() {
      super()
      this.state = {
        items: [],
        visited: [{name: "This Drive", path: "@back", root: ""}]
      }

      this.handleFolderClick = this.handleFolderClick.bind(this)
      this.handleFileClick = this.handleFileClick.bind(this)
    }
    componentDidMount() {
      if (this.props.url.length === 0) return
      fetch(this.props.url)
      .then(res => res.json())
      .then(items => this.setState({ items }))
    }
    render() {
      const folders = this.state.items.map((item) => {
        if (!item.isfile) {
          return <Card handleClick={this.handleFolderClick} root={item.root} path={item.path} isfile={item.isfile} name={item.name}     size={item.size}/>
        }
      })
      const files = this.state.items.map((item) => {
        if (item.isfile) {
          return <Card handleClick={this.handleFileClick} root={item.root} path={item.path} isfile={item.isfile} name={item.name} s    ize={item.size}/>
        }
      })
      const pathButtons = this.state.visited.map((item) => {
        return <PathButton handleClick={this.handleFolderClick} root={item.root} path={item.path} name={item.name}/>
      })
      return (
        <div>
          {pathButtons}
          <div className="flex-container">
            {folders}
            {files}
          </div>
        </div>
      )
    }
}

Essentially the issue is that the HermesWorker component is not being rerendered to use the new url prop. I am not sure why this is happening because for example, in the hermesworker it renders other subcomponents that do get rerendered during a state change.

Any information is appreciated

EDIT updated to add hermes worker, the file is over 100 lines so i cut out and only pasted the stuff I thought was important to the issue, can supply more if needed

Answer 1

I tested that code and it seems to be working fine. Could you provide What is set in HermesWorker component?

Edit: You'll require to set your state with setState on component updates. To do this, you may look for componentDidUpdate , which will run on every update. This is different from componentDidMount , which (hopefully) will run once and then the component may update and re-render, but re-render it's not considered as "mount". So you may try this instead:

constructor(props) {
  super(props);
  this.state = {
    url: '',
    items: [],
    visited: [{name: "This Drive", path: "@back", root: ""}]
  }
  this.fetchData = this.fetchData.bind(this);
}
componentDidMount() {
  //Mount Once
}

componentDidUpdate(prevProps, prevState) {

  if (this.state.url !== this.props.url) {
    this.setState({url: this.props.url});
    // Url state has changed.
  }
  if(prevState.url !== this.state.url){
    //run your fetch
    this.fetchData();
  }
}
fetchData(){
  if (this.props.url.length === 0) return
  fetch(this.props.url)
  .then(res => res.json())
  .then(items => this.setState({ items }));
}

Note: I moved the fetch to its own function, but that's completly up to you.

Also notice i added url to the state. Make sure to keep your props set to avoid unexpected behaviours.

Edit 2: componentDidUpdate will hand you prevProps and prevState as parameters. With prevProps you get access to whatever props you got on the previous update, and with prevState , as you may guess, you get access to whatever-your-state-was on the previous update. And by "on the previous update" i mean before the update got executed.